A production tree 10-1 of the prior art illustrated in FIG. 1 installs on a tubing head adapter 16 connected to a tubing head 12. Such a production tree 10-1 is often referred to as a Christmas tree. An upper master gate valve 20 connects above a lower master gate valve 18. A studded cross 22 mounts to the top of the upper master gate valve 18, and a top connector 14 connects to the top of the studded cross 22. As is typical, a flow line gate valve 24 and a kill line gate valve 26 connect to opposite sides of the studded cross 22, and the gate valves 24 and 26 connect to additional components (e.g., piping, chokes, etc.).
The master gate valves 18 and 20 can be closed to seal off the wellbore. The flow line gate valve 24 and the kill line gate valve 26 are used to control the flow line and kill lines (not shown). The top connector 14 can be removed to provide access to the wellbore for various operations. For example, a coil tubing assembly (not shown) or a wireline lubricator and valve assembly (not shown) can be positioned on the studded cross 22 in place of the top connector 14. Such accessory assemblies can be used to inject chemicals, to carry downhole sensors and tools, or to perform a variety of other operations.
Another assembly illustrated in FIG. 2 is a Y-body Christmas tree 10-2, such as disclosed in U.S. Pat. No. 6,851,478. The Y-body tree 10-2 has a body 30 formed as a single piece of steel that has a vertical bore 31 extending axially therethrough. The body 30 connects to a first shut-off valve 18 that is attached to a tubing head adapter 16 and a tubing head 12. The body 30 houses a second shut-off valve 32 for opening and closing the vertical bore 31. The body 30 also has gate valves 24 and 26 attached to an upper, flow tee portion 33 of the body 30 that communicates with the vertical bore 31. At the top of the vertical bore 31, the body 30 has a top cap 14 attached. A coil tubing bore 34 on the body 30 connects to the vertical bore 31 below the upper shut-off valve 32 in the body 30 and allows coil tubing CT to be inserted and suspended through the lower shut-off valve 18 and not the upper shut-off valve 32.
Yet another assembly illustrated in FIGS. 3A-3B is a Christmas tree 10-3 having integrated gate valves, such as disclosed in US 2008/0029271. In particular, a tubing head adapter 16 attaches to a tubing head 12, and an integral body 40 attaches to the tubing head adapter 16. A flow tee 22 attaches atop the integral body 40, and gate valves 24 and 26 and a top cap 14 attach to the flow tee 22 in a conventional manner.
The integral body 40 houses a lower shut-off valve 42 and an upper shut-off valve 44 therein. For instance, the integral body 40 depicted in cross-section in FIG. 3B is composed of a large block of material having the valves formed therein. As shown, such an integral body 40 can be used for a surface tree, but is often used for subsea trees too. Inside, the body 40 can house a coil tubing assembly 45 supported in bore 41 by lock down pins 46 and connected to a feed line 48 with a connector.
Similar to the tree 10-3 of FIGS. 3A-3B, another form of Christmas tree is a solid block tree that has a single, solid-forged body and integrated lower and upper master valves. This body also has integrated wing valves and a swab valve. Such a tree offers the advantage of being compact.
Each component of such trees 10 must be configured for the desired through-bore of the trees 10, and all of the flanged connections between components must be configured for the required pressure rating of the tree 10. This requires careful design of the tree and a necessary inventory of the components to build the tree 10 in the field. In general, what is needed in the art are production trees that are more versatile in both design and assembly.